The present disclosure makes reference to fourteen documents identified in the list of References below. For the sake of brevity, the references are each numerically identified by bracketed numbers (e.g., [1]) in the order in which they are identified in the list of References. The entire disclosures of References [1]-[14] are incorporated herein by reference.
The use of power converters in grid-connected applications has increased in recent years. Renewable energy sources have become a more and more attractive option for producing electrical energy. Instead of larger plants, electrical energy can be produced in a distributed manner using renewable energy sources, such as solar power and wind power, for example. In distributed generation systems, power converters act as an active interface between the power supply and a power grid.
In most cases, electrical energy from photovoltaic panels (PV panels) and wind turbines may have to be converted to a suitable form for consuming it or for feeding it to the grid. The conversion of electrical energy should be carried out with high efficiency so that losses occurring during the conversion are kept minimal. The electrical energy may be converted to alternating voltage having a fixed amplitude and frequency so that the energy can be fed to the grid or consumed directly with appliances that can be operated with the grid voltage.
The power converters may be voltage source inverters (VSI) or current source inverters (CSI) connected to the grid by means of L, LC or LCL passive filter [1]-[8]. Originally, a simple L filter was sufficient, but converters with more complex filter structures are becoming more popular because of their improved characteristics allowing compliance with increasingly more restrictive standards.
Systems with more complex filters, however, also present more complex dynamics. In addition to the increased complexity, an issue of a resonance may arise, which may compromise stability of a system and make the system more susceptible to grid disturbances.
Therefore, more sophisticated controller methods would be beneficial in order to guarantee stability while having an enhanced disturbance rejection capability. In particular, the control schemes may have to be able to attenuate the harmonics distortion. Attenuation of the harmonic distortion has become an almost mandatory feature for controller design. At the same time, it would be desirable to keep the implementation of such controllers as simple as possible and without the requirement of additional sensors in order to keep the implementation cost comparable to known L filter-based converters.